1. Field of Invention
This invention relates to appliances with internal lids for closing and sealing tubs located with the appliances, and in particular this invention relates to a dishwasher that includes an internal wash tub lid and a seal assembly for sealing a wash tub lid onto a wash tub.
2. Description of the Prior Art
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.
Automatic dishwashers are well known in the art. The operation of the majority of dishwashers is similar and can be summarised as follows: Dirty dishes are placed in a wash compartment or wash tub. Once the dishes have been placed in the wash tub, the dishwasher is closed. The dishwasher closing action normally also seals the wash tub. When the wash cycle is started, hot water mixed with detergent is sprayed into the tub to clean the dishes. This is followed by a clean water spray to rinse the dishes.
The two most common types of dishwashers are front opening (drop-down door—the door pivoting outwards and downwards about its lower edge) or drawer-style. In drawer-style dishwashing machines, such as the Fisher and Paykel DISHDRAWER®, the wash tub is an open-topped compartment. Dirty dishes to be washed are stacked in racks in the tub. The main body or chassis of the dishwasher includes a tub lid, the tub lid having a perimeter seal. When a user pushes the drawer back into the casing of the dishwasher, a mechanism such as a cam lowers the lid and perimeter seal downwards onto the open top, pressing the perimeter seal onto the perimeter of the tub to close and seal the tub. The cleaning and rinsing water is sprayed upwards into the compartment from a spray arm on the base of the tub. An example of an open-top wash tub and lid sealing arrangement is disclosed in EP 1661504.
One problem that is well-known in the art is that of providing a reasonable or sufficient seal between the lid and the tub, especially during the wash cycle. During the wash cycle, the action of mechanical components such as the spray arm can cause the tub and lid to vibrate, potentially breaking the seal. If the seal is not maintained, water can leak from the wash tub during the wash or rinse cycles. This can cause mess or damage, and be inconvenient to a user.
Furthermore, when open-topped wash compartments or tubs are used, it is easy for a user to inadvertently overload the tub, making the seal between the lid and the tub harder to maintain. For example, if large dishes or cooking pots are placed in the wash tub, a user must ensure that these are positioned so that they do not extend above or overhang the top edge of the tub. This extension or overhang makes it difficult for a seal to be created or maintained around the top edge of the tub, as the lid cannot be pressed fully down onto the rim or edge of the tub to create the seal between the two. It can be difficult to detect or correct an overload situation when the tub is loaded in such a manner that a seal between the lid and the tub is initially created, but where the load is positioned such that movement and vibration during the wash cycle can act to break the seal.
One embodiment of the design disclosed in and shown in EP1661504—specifically, the arrangement shown in FIG. 39 of EP1661504—is intended to overcome this problem by providing a separate seal support carrier 252, interposed between the periphery or edge of the lid 217 and the seal. The lid 217 is attached to the inner surface of the top of the dishwasher casing or chassis. The main body or planar horizontal upper portion of the lid 217 remains stationary, attached to the dishwasher frame or chassis. As shown in FIG. 39, the seal is attached to the support carrier 252, with the support carrier 252 and the attached seal lowered onto the upper edge or periphery of the tub to create a seal between the tub and the lid. This arrangement can help to overcome the sealing problems outlined above. However, it is necessary for the seal carrier to extend (to form the seal) and retract (when the dishes are unloaded and the tub is withdrawn from the chassis) for every wash cycle. This extension/retraction cycling can fatigue the support carrier 252.
It is also desirable to minimise the amount of rigid structure contained in the chassis, which is used to hold the lid and seal in place relative to the tub. Rigid structure between the tub and the chassis can provide a noise transmission path from the tub to the casing, and it is desirable to minimise as far as possible the potential noise transmission path(s), as this can be disruptive or disturbing to a user. This can also add cost, weight and complexity to a dishwasher structure.
It can be seen that a mechanism which helps to reduce the extension cycles of the seal and the associated structure is desirable. A structure which helps to reduce the number of potential noise transmission paths from the wash tub, by minimising the amount of rigid structure on the casing, which also has the benefit of simplifying the construction and avoiding the need for additional overall weight is also desirable.